9. Hydrogen is 99% H, 0.8% ?H, and 0.2% H. Calculate its average atomic mass.

 Technically, this cannot be answered, since none of the H atoms have a mass number assigned.  With the assumption noted delow, I calculate 1.012 as the average atomic mass.

Explanation:

My answer is based on assumed masses for the three H isotopes:

1H :   1 AMU

2H:   2 AMU   Deuterium

3H:    3AMU   Tritium

     AMU   Rel Abund.    Wt. Avg

1H1     99.00%      0.99

2H2       0.80%      0.016

3H3       0.20%       0.006

              Sum   1.012

the dissolution of polymer can be thermodynamically described in 2 steps.